Monday, July 11, 2016

All You Wanted to Know About Electron Microscopy...But Didn't Dare to Ask!

What Is Electron Microscopy?
One of the earliest and significantly powerful microscopes was a light microscope created by Antony van Leeuwenhoek. This microscope was made up of a powerful convex lens and an adjustable specimen holder. It's suspected that this microscope was able to magnify objects up to 400x, leading van Leeuwenhoek to discover protozoa, spermatozoa, and bacteria. 

The first limitation with van Leeuwenhoek's microscope was the quality of the convex lens, but that could easily be fixed by adding another lens to magnify the image produced by the first lens. This configuration gives us the compound microscope, the basis of modern light microscopes. Today's light microscopes can give us a magnification of up to around 1000x, but they were limited by the wavelength of the light used for illumination. Small improvements to magnification could be reached using a smaller wavelength of light (blue or ultraviolet) or by dipping the specimen and the front of the objective lens in oil (which has a high refractive index). 

Then, in the 1920s, accelerated electrons in a vacuum were found to behave just like light, except they had a wavelength about 100,000 smaller than that of light. This meant that they could be used for higher magnifications than light. Instead of being manipulated by glass lenses and mirrors, electrons could be manipulated using electric and magnetic fields; giving rise to the first transmission electron microscope (TEM) built by Dr. Ernst Ruska at the University of Berlin. 

The TEM has a resolving power of 0.1 nm, meaning that using the microscope, we are able to tell the difference between two points down to 0.1 nm (Points less than 0.1 nm apart will be seen as a single point). This is significantly powerful magnification, compared to the resolving power of the naked eye in proper light, which is 0.2 mm.

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